How much sleep do you need?
- Adults (18 to 64): 7 to 9 hours.
- Older adults (65+): 7 to 8 hours.
- Teenagers (14 to 17): 8 to 10 hours.
- School-age children (6 to 13): 9 to 11 hours.
These ranges come from expert consensus panels in the United States. Individual needs vary slightly, but regularly sleeping less than 7 hours is associated with health risks in adults.
What happens after one night of 4 hours
- Tiredness and sleepiness during the day.
- Poorer attention, memory and decision-making.
- Slower reactions, with a higher risk of accidents.
- Irritability and lower mood.
- More cravings for sugary, high-calorie foods.
One short night is not dangerous for most people, but avoid driving or risky tasks if you feel sleepy.
Sleep debt: when short nights add up
In a well-known laboratory study, people restricted to 4 or 6 hours of sleep a night for two weeks showed steadily worsening attention and memory, reaching levels similar to one or two nights without sleep. Yet they rated themselves as only slightly sleepy. This shows that people often do not notice how impaired they are.
Long-term effects of short sleep
- Higher risk of road and work accidents.
- Weight gain and obesity.
- Type 2 diabetes.
- High blood pressure and heart disease.
- Weakened immune response.
- Anxiety and depression.
What about natural short sleepers?
A very small number of people carry rare genetic variants that allow them to feel well and function on about 6 hours or less. They are rare; most people who believe they need little sleep are building up sleep debt, often catching up at weekends.
Can you catch up on sleep?
Sleeping longer after a short night helps you recover from acute tiredness, but repeatedly catching up at weekends does not fully reverse the effects of chronic short sleep, and it can shift your body clock, making Monday mornings harder. A regular sleep schedule is better.
Do naps help?
A short nap of 10 to 20 minutes can improve alertness after a short night. Longer naps or naps late in the day can cause grogginess and make it harder to sleep at night.
Why you may still be tired after 8 hours
- Poor sleep quality or frequent waking; see fragmented sleep.
- Sleep apnoea, especially with snoring or choking; see choking in sleep.
- Irregular sleep times or shift work.
- Alcohol or caffeine late in the day.
- Depression, anxiety or stress.
- Anaemia, underactive thyroid, diabetes or other medical conditions.
- Some medicines.
Tips to get more and better sleep
- Keep a regular bedtime and wake time, even at weekends.
- Protect a sleep window of at least 7 to 8 hours in bed.
- Get daylight in the morning.
- Limit caffeine after midday and avoid alcohol before bed.
- Wind down for an hour without screens.
- Keep the bedroom dark, quiet and cool.
If you cannot sleep more
If you have the chance to sleep but cannot, this may be insomnia. Cognitive behavioural therapy for insomnia (CBT-I) is the most effective long-term treatment and is more effective than sleeping tablets.
See insomnia.
Short sleep before exams or deadlines
Pulling an all-nighter or sleeping only 4 hours before an exam usually reduces performance, because sleep is needed for memory consolidation and concentration. Spreading study over days and protecting sleep the night before gives better results.
When to see a doctor
- You are falling asleep while driving or at work.
- Loud snoring, choking or pauses in breathing at night.
- Persistent tiredness despite enough sleep.
- Insomnia lasting more than 3 months.
- Low mood, anxiety or thoughts of self-harm.
Key points to remember
- Four hours is not enough for almost all adults.
- Most adults need 7 to 9 hours.
- Chronic short sleep impairs performance and health, often without you noticing.
- Tiredness after 8 hours may signal a sleep or medical problem.
Questions about short sleep
These answers are general information and do not replace an examination or individual medical advice.
Is 4 hours of sleep enough for one night?
You can get through one night, but you will be less alert and should avoid driving if sleepy.
Is 5 hours of sleep enough?
Not for most adults on a regular basis.
Can your body adapt to less sleep?
You may feel used to it, but tests show performance stays impaired.
What happens if you sleep 4 hours a night for a week?
Attention, memory, mood and reaction times worsen progressively.
Why am I still tired after 8 hours of sleep?
Poor sleep quality, sleep apnoea, stress, depression or medical conditions may be the cause.
Is it better to sleep 4 hours or stay awake?
Some sleep is better than none.
Can you make up for lost sleep?
Partly, but regular sleep is better than catching up.
How much sleep do teenagers need?
Around 8 to 10 hours.
Are there people who need only 4 hours?
True short sleepers are very rare.
Sources
- Watson NF et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and SRS. J Clin Sleep Med. 2015
- Hirshkowitz M et al. National Sleep Foundation’s sleep time duration recommendations. Sleep Health. 2015
- Van Dongen HPA et al. The cumulative cost of additional wakefulness. Sleep. 2003
- NHS · Insomnia
This guide is for general information and does not replace medical advice. How a problem is diagnosed and treated depends on your examination and medical history. If you think you have an emergency, contact your local emergency services.